For bi-directional communication buses, both the driver and receiver have to accommodate not only the supply voltage variation of each of the drivers attached to the communication bus, but also any possible ground bounce between the drivers. The latter may be especially the case if the drivers reside in different electrical units. This implies that even for the case of the voltage levels of the generated bus signals lying between a supply voltage level and ground, the voltage on the communication bus could vary by a multiple of the supply voltage. For the particular case of the Controller Area Network (CAN) standard, the generated H and L bus line voltages lie between 0.5V and 4.5V, while the sensed signals reach from −2V to +7V and resilience of the drivers to signal voltages from −3V to +16V is required.
The small required voltage range of the applied bus line signals for the CAN transceiver would make the CAN transceiver an ideal candidate for implementation on a low-voltage digital CMOS process. Unfortunately, presently available low-voltage Complementary Metal-Oxide-Semiconductor (CMOS) integrated circuit architectures fail to cope with the large possible voltages on the CAN bus. Consequently, conventional CAN transceivers are manufactured in special high-voltage CMOS or bipolar processes.
While radiation hard low-voltage (e.g. 3.3V) digital CMOS processes are available, the presently available accommodated voltage range for these radiation-hard digital CMOS processes is limited and non-compliant even to the minimum required CAN bus voltage levels (i.e. from −2V to +7V). Thus, conventional CAN drivers cannot be realized using such low-voltage digital CMOS processes, simply because the gate-drain voltage in forward bias would be too large for the transistors involved in this type of CMOS processes. Accordingly, conventional CAN driver implementations use high voltage transistors and protection diodes.
On the other hand, presently available high-voltage CMOS processes, which would allow for the implementation of CAN standard compliant transceivers, are not radiation tolerant.
Thus, there is a need for a radiation-hard driver structure for a bi-directional communication bus (e.g. a CAN bus) that may be implemented in a low-voltage digital CMOS process. There is a further need for radiation-hard tri-state driver circuits and bi-state driver circuits for a bi-directional communication bus (e.g. a CAN bus) that may be implemented in a low-voltage digital CMOS process.